1. Field of the Invention
The present invention relates to a charge pumping circuit and method, more particularly, to a dual edge modulated charge pumping circuit and method.
2. Description of the Related Art
FIG. 1(a) is a schematic diagram showing a conventional charge pumping circuit 10. Referring to FIG. 1(a), the conventional charge pumping circuit 10 primarily has a first capacitor C1, a second capacitor C2, and a switch combination circuit. More specifically, the switch combination circuit consists of a first switch S1, a second switch S2, a third switch S3, and a fourth switch S4. The first switch S1 is coupled between an input voltage Vin and a first electrode NA of the first capacitor C1. The second switch S2 is coupled between the first electrode NA of the first capacitor C1 and a ground potential. The third switch S3 is coupled between the input voltage Vin and a second electrode NB of the first capacitor C1. The fourth switch S4 is coupled between the second electrode NB of the first capacitor C1 and an output terminal OUT. The second capacitor C2 has a first electrode NC coupled to the output terminal OUT, and in turn also coupled to the fourth switch S4. The second capacitor C2 has a second electrode ND coupled to the ground potential.
The operation of the conventional charge pumping circuit 10 includes a first phase and a second phase. During the first phase, the first and the fourth switches S1 and S4 are both turned OFF and the second and the third switches S2 and S3 are both turned ON, such that the first electrode NA of the first capacitor C1 is coupled to the ground potential and the second electrode NB of the first capacitor C1 is coupled to the input voltage Vin. As a result, the first capacitor C1 is charged during the first phase so as to develop a potential difference of Vin across the second and the first electrodes NB and NA. Thereafter followed with the second phase, the first and the fourth switches S1 and S4 are both turned ON and the second and the third switches S2 and S3 are both turned OFF, such that the first electrode NA of the first capacitor C1 is coupled to the input voltage Vin and the second electrode NB of the first capacitor C1 is coupled to the output terminal OUT. As a result, the voltage at the second electrode NB of the first capacitor C1 is abruptly pulled from Vin up to 2*Vin at the beginning of the second phase. Through the conductive fourth switch S4, this voltage 2*Vin is applied to the output terminal OUT such that the conventional charge pumping circuit 10 may effectively provide an output voltage of 2*Vin.
The charge pumping circuit 10 shown in FIG. 1(a) has a shortcoming with respect to the only capability of providing an output voltage Vout fixed at 2*Vin. In order to generate an adjustable output voltage Vout within a range from Vin to 2*Vin, a linear voltage regulator 11 must be additionally provided between the first electrode NC of the second capacitor C2 and the output terminal OUT, as shown in FIG. 1(b). Based on a predetermined reference voltage Vref, the linear voltage regulator 11 converts a pumping voltage Vpp at the first electrode NC of the second capacitor C2 into an output voltage Vout between Vin and 2*Vin. Although the linear voltage regulator 11 effectively converts the fixed pumping voltage Vpp into the adjustable output voltage Vout between Vin and 2*Vin, the linear voltage regulator 11 causes a reduction to the power converting efficiency and thus wastes energy.